This invention relates to methods for implanting prosthetic devices in humans or animals. More particularly, it relates to a method for implanting a prosthetic device wherein it is desired to incorporate the prosthetic device permanently beneath an epithelial surface. The methods of the invention can be applied to subepithelial implantion of prosthetic devices such as contact lenses, dermal devices, dental devices otolaryngological devices, vascular access and ostomy devices. The invention also relates to methods of treating prosthetic devices and to treated devices produced thereby, which allow the devices to be implanted permanently below the epithelial layer.
There are a number of prosthetic devices which necessarily or desirably can be implanted either completely or partially beneath epithelial tissues. It is to be understood that reference to "epithelial" tissues herein includes epidermal tissue as well as other epithelial tissues. Implantation beneath the epithelium may be done for purposes of fixation of the device relative to other tissues and/or for cosmetic purposes. Examples of implanted prostheses include dental prostheses such as artificial teeth and bridgework; hearing aids; dermal implants; vascular access devices, such as those associated with hyper-alimentation; colostomy devices; and prosthetic corneas, which can be made of synthetic or naturally-derived materials. While the methods of the invention will be described specifically with reference to their application in subepithelial implantation of prosthetic corneas, it will be readily understood that they can be applied any time one desires to implant a prosthetic device partially or completely beneath a viable epithelial surface.
Advantageously, the methods of the invention can be employed in the field of ophthalmology. Ophthalmologists have long been concerned with the treatment of vision problems caused by defects in the cornea. The most common of these problems are nearsightedness, which can be caused by excessive corneal curvature; farsightedness, which can be caused by insufficient corneal curvature; and astigmatism, which is caused by corneal asymmetry. Traumatic injury to the cornea with resultant scarring and/or distortion of corneal tissue, can also cause vision problems. Frequently, corrective lenses such as eyeglasses or contact lenses can be employed to correct common vision problems. In certain severe conditions, however, or where there has been damage to the cornea, or in the case of contact lens intolerant patients, surgical procedures must be employed to correct the geometry of the cornea. Although a number of these surgical procedures, known generally as refractive keratoplasties, have been developed, consistently good results have not been obtained. Consequently, these procedures have not been widely employed.
A number of refractive keratoplasty procedures employ the implantation of geometrically altered corneal tissue obtained from donor corneas or from the patient's own cornea to obtain refractive correction. In one such procedure an anterior portion of the patient's own cornea is removed. The removed corneal section is reshaped on a cryolathe in order to reduce or increase the amount of curvature. The cornea is then allowed to thaw and it is stitched back into place on the corneal surface. In another procedure, a donor cornea that has been shaped on a cryolathe is used to replace an anterior portion of the patient's cornea that has been surgically removed.
In another refractive keratoplasty procedure, only the epithelial layer of the patient's cornea is removed. A donor lens "button" that previously has been frozen and ground to the desired degree of refraction, is then sewn in place.
U.S. Pat. No. 4,346,482, issued to Tennant et al., describes a method for correcting vision in which a circular portion of a donor cornea is anteriorly shaped for refractive correction of the patient's vision. The posterior surface of the corneal section is ground to correspond to the curvature of the patient's cornea. The lens includes a posteriorly directed integral ring which is inserted into the patient's cornea. The donor cornea is preserved by a freezing process which kills keratocytes, such that only collagen is left for fixation. The procedure relies on migration of keratocytes from the patient's tissues into the donor cornea for healing and incorporating the donor cornea into the eye.
All of the foregoing procedures, which use donor corneas or the patient's own corneal tissue, rely on extremely precise and delicate cutting procedures. Even using sophisticated equipment that is available for this purpose, it is difficult to assure the required degree of refractive correction. Where donor corneas are to be used, the supply of donor corneas is extremely limited, due to social and religious mores which make it difficult to obtain corneas from cadavers. In the event that these procedures fail, for example, because of tissue rejection, infection, improper healing or inadequate refractive correction, it may be difficult to obtain additional biocompatible material to perform corrective surgery. Yet another drawback to these procedures is the inherent difficulty of working with biological materials, which have a limited useful lifetime and require special handling procedures to keep them in viable condition.
A number of refractive keratoplasty procedures have been developed which employ corneal prostheses made from synthetic materials or from non-living materials derived from natural sources such as collagen. U.S. Pat. No. 4,581,030, issued to Bruns et al., discloses a prosthetic replacement for the cornea, particularly a transparent collagen material useful for making such a prosthesis and to methods for making the transparent collagen material. The prosthetic cornea comprises collagen, polyhydroxyethylmethacrylate or vitrosin.
U.S. Pat. No. 3,454,966, issued to Rosen, discloses a corneal transplant structure of synthetic material compatible with body tissues as a replacement for a removed section of the cornea. The outer marginal portion of the structure is in intimate contact with the marginal rim of the cornea surrounding the structure. A controlled temperature is applied to the structure around the area of its contact with parts of the cornea to facilitate attachment.
A number of papers have been published which describe the use of tissue adhesives such as cyanoacrylate adhesives to "glue" synthetic contact lenses onto the corneal surfaces (see, e.g., Richards, J. S., Can J Ophthalmol., 6(2):98-103 (1971); Ruben, M., Trans. Ophthalmol. Soc. U.K., 90:551-564 (1970); Dohlman, C. H., Arch. Ophthalmol., 83(1):10-20 (1970); Dohlman, C. H., Trans. Am. Acad. Ophthalmol. Otolaryngol., 73(3):482-493 (1969)). The synthetic lenses are generally made of acrylate polymers such as polyhydroxyethylmethacrylate.
The aforementioned procedures, in which synthetic or collagen contact lenses are affixed to the corneal surface, overcome some of the previously discussed problems inherent in keratoplasty using donor corneas or the patient's own corneal tissue. Difficulties are encountered with synthetic lenses, however, inasmuch as it is difficult to assure that they will be permanently incorporated into the patient's eye without infection or rejection. One procedure which has been proposed to overcome this problem involves making an incision in the stromal tissues of the cornea to form a pocket into which a synthetic lens is placed. This procedure has been successfully used to increase refractive power in rabbits (McCarey, B. E. and Andrews, D. M., Invest. Ophthalmol. Vis. Sci., 21:107-115 (1981)). In primates, however, the Bowman's membrane, which is relatively rigid, causes the cornea to resist any increase in curvature induced by the implanted lens. Koenig and coworkers attempted to correct this problem by making a series of relaxing incisions in the Bowman's membrane (Ophthalmic Surg., 15:225-229 (1984)).
There is a need in the field of ophthalmology for a reliable procedure whereby synthetic lenses for refractive correction can be permanently implanted and incorporated into the tissues of a patient's eye. Furthermore, there is a need generally for procedures whereby prosthetic devices can be permanently implanted and incorporated beneath epithelial tissues in humans or animals.